Presently Taiwan generates a great amount of daily waste such as ashes, industrial discarded soils, industrial wastes, discarded solid materials, waste oil, waste solution, discarded liquid, sludge, other liquid type wastes, etc. On the other hand, gravel used in construction projects is generally made by crushing stones and rocks excavated from rivers or mountains. They are called natural gravel for building bridges and roads and used as fillers in the civil engineering and construction projects to increase the strength and rigidity of reinforced concrete or asphalt roads. As the natural gravel is excavated from nature, their surfaces are contaminated with organic substances and bacteria. As a result, corrosion often occurs to the asphalt road surface that contains gravel, and the asphalt road surface tends to crack and damage. Moreover, natural gravel has different compositions. After crushing to a small rock fragments, the inner tissue is destroyed and the strength decreases significantly. This also reduces the pressure resistance and loading power of the concrete structure and shortens the service life. This is a big drawback of natural gravel. Furthermore, with increasing awareness of environmental protection and conservation, excavating the rivers to get the natural gravel often results in loss of soil, unbalances the ecosystem, and causes serious damage to the natural environment, thus it is neither sustainable nor commendable in the long run.
In addition, with the fast progress of industrial and commercial developments, and increased living standards, a great deal of advanced products has been produced to meet people's requirements. These products often involve complicated manufacturing processes and generate a great amount of waste. This waste has become a serious threat to the environment. Hence processing discarded soil and industrial wastes has become an important and urgent issue. Otherwise as industry and commerce thrives, the environment rapidly deteriorates.
Therefore to produce an environment-friendly building material and recycle hazardous ashes, slag, industrial wastes, discarded soils, discarded solid materials, waste oil, waste solution, discarded liquid, sludge, other liquid type wastes and the like to become reusable products that have economic value so that the resources may be reclaimed, and second preventing a public hazard has become a highly pursued goal for nearly every country around the world. This issue is especially prevalent in Taiwan because of the increased awareness of environmental protection and new environmental protection regulations. Moreover, the general public has a great aversion toward treatment of hazardous industrial wastes, ashes, discarded soil (sludge), and land resource is limited, to locate desired landfill is increasingly difficult, and hazardous wastes are not permitted to be dumped in landfill sites. Some wastes such as industrial wastes, ashes, and discarded soil (sludge) are contaminated with hazardous heavy metal and dioxins, they are very difficult to treat and handle.
The conventional treatment approach for hazardous ashes, industrial wastes, discarded soil (sludge) generally is to dump into a landfill or incinerate to reduce volume and weight. Disposing industrial wastes and discarded soil without a thorough plan, or simply dumping ashes and slag into landfills will result in harmful substances seeping underground polluting water. To use slag as road material, sea barrier and building concrete will generate toxic dust when the road and building are cutaway or damaged because the hazardous materials are usually permanent heavy metal, or dioxins and polychlorinated biphenyl. Discarding of construction, industrial wastes and soils often creates a second public hazard. It causes an environmental pollution that has harmful effect to human health. Hence discarding or dumping the wastes into landfills cannot thoroughly resolve the problem. Residual dioxins in the ashes produced by the incinerators are also difficult to treat and handle. All these problems remain to be overcome.